1. Field of the Invention
The present invention relates to position measuring devices that generate quadrature data signals, for the purpose of position and/or speed control of various devices, using optical sensors, for example.
2. Discussion of Related Art
As shown in FIG. 1, it is known to couple a position measuring device, such as an angle encoder 10, to a motor 12, such as a brushless motor, as described in U.S. Pat. No. 5,936,236, the entire contents of which are incorporated herein by reference. The angle encoder 10 includes a scale 14, a hub 16 and a scanning unit 18. The hub 16 is coupled to the motor 12 via a shaft 20 so as the motor 12 rotates, so does the scale 14. The encoder is used to encode the commutation of the motor. The scale 14 has three graduation tracks 22, 24, 26 disposed thereon. The angle encoder is an optical encoder and graduation tracks 22, 24, 26 are formed by opaque and light transmissive areas sequentially arranged. The scanning unit 18 includes a plurality of scanning elements that scan the graduation track 22, 24 and 26.
The scanning unit 18 outputs three analog scanning signals S1A, S2A, S3A. These analog signals are input to a comparison unit 28 where they are converted to digital signals. For commutation signals each of the scanning signals are converted into a digital signal that can be synchronized with the relative position of the motor's windings. In addition, the outputs of the comparison unit 28 are sent to the motor 12 through a drive circuit 30. Position commands are generated by a controller 32 which acts upon measurements made by a feedback device 34.
One disadvantage of the position measuring device of FIG. 1 is that in the case where the circuitry includes a data array of a standard Opto-ASIC, the encoder resolutions available for data output signals are limited to those scales that have a count that closely matches the design of the array. Therefore, only certain counts can be provided. The only way for providing a user with a custom count is to design a new ASIC for that particular count.
Another disadvantage of the measuring device of FIG. 1 is that the commutation circuitry generates signals that are suitable only for the control of the commutation of electrical brushless motors. This type of signal is not suitable for data applications. Therefore, the commutation portion of the device cannot be used to generate custom count data signals using the standard scale.